Evaluation of the Antioxidant Activities of Psidium guajava and Aloe vera

This paper aimed to study the antioxidant properties of two Nigerian plants Psidium guajava (guava) Myrtaceae and Aloe vera Liliaceae plants which have a broad application in phytomedicine. The plants were assessed by quantifying their individual chemical contents and their 1:1 (mass/mass) homogenous combination (guava+A. vera) simultaneously. The non-antioxidant phytochemical quantified included total alkaloids. There was a significant difference in the total alkaloids content (measure on dry weight basis, mg/g) in the analysed plant materials in the order of guava (111.13±0.45)>guava+A. guava (65.99±0.37)>A. vera (22.86±0.15). The antioxidant properties measured were the levels of total phenol, tannin, total flavonoid, total saponin, vitamin C, 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging ability and trolox equivalent antioxidant capacity (TEAC). P. guajava recorded significantly higher (p<0.05) antioxidant phytochemicals contents than A. vera except for vitamin C where it recorded significantly lower (p<0.05) value. There was no significant difference (p>0.05) in the vitamin C contents of A. vera and the combined plant materials, guava+A. vera. Guava had also significantly higher (p<0.05) DPPH scavenging ability (0.056 mg/ml), and TEAC (12.51±0.40 mM/gdw) than A. vera. The combined plant materials guava+ A. vera showed synergistic properties in the DPPH free radical scavenging ability (0.15 mg/ml) and antagonistic activity in the TEAC (4.58±0.17 mM/gdw). This study suggests that while guava may be a better antioxidant than A. vera when used separately, the combined plant materials produces synergistic antioxidant interaction, which could be used to enhance their medicinal applications.